Process for producing cyclohexane



Jan. 7, 1969 F. r. SHERK ETAL.

TOLU ENE 23 SSEPARATOR Y Z 7 3 Ha I n/REACTOR I? I4 5 I5 Iii L J DEMETHYLATION zous f FRACTIONATOR 2| 5 SEPARATOR INVENTOR F. T. SHERK J. F. H U T To BY f w- M 4.

A 7' TORNEYS United States Patent PROCESS FOR PRODUCING CYCLOHEXANE Fred T. Sherk and John F. Hutto, Bartlesville, 0kla.,

assignors to Phillips Petroleum Company, a corporation of Delaware Filed Aug. 19, 1966, Ser. No. 573,578

US. Cl. 260-667 Int. Cl. C07c 3/58; C07c 13/18 This invention relates to the production of cyclohexane. In one aspect it relates to the production of cyclohexane through a demethylation of methylcyclohexane.

cyclohexane has been previously made as a byproduct in the fractionation of natural gasoline. However, this supply may be inadequate to meet the rising future demands since an increased demand for high purity cyclohexane has resulted from the continued growth of the polyamide fiber markets. Therefore, attempts have been made to augment the supply of cyclohexane by ring closure reactions of straight chain hydrocarbons; however, these processes have not been fruitful. Many such processes have been proposed, patented or used for the production of cyclohexane. Attention has been given in particular to the catalytic hydrodealkylation of toluene to benzene followed by the hydrogenation of benzene to produce the cyclohexane products; however this process has not enjoyed widespread acceptance because it entails the use of expensive catalysts and gives rise to the attendant problems of coke laydown, catalyst fines separation, catalyst deactivation and requires large quantities of hydrogen for eflicient operation. Another possibility is the demethylation of methylcyclohexane to give methane and cyclohexane as the principle products. As this route is more direct than the preparation of benzene from toluene demethylation followed by hydrogenation, it offers a potentially cheaper method of producing cyclohexane. The problem with this reaction is that it results in a number of side reactions and the yield of cyclohexane is well below 50 percent by weight.

Therefore, an object of this invention is to provide a process for producing cyclohexane from the hydrogenation of toluene followed by the demethylation of the methylcyclohexane wherein the efiiciency of the reaction is greatly improved to produce a higher yield of cyclohexane.

Another object of our invention is to carry out the demethylation of the methylcyclohexane under conditions which will increase the formation of toluene as a side product.

Another object of this invention is to provide a method which takes advantage of the toluene produced in the demethylation of methylcyclohexane to cyclohexane in order to increase the overall efficiency in the production of cyclohexane.

Other objects and many of the attendant advantages of this invention will be readily appreciated as the same becomes better understood by reference to the following detailed description which is considered in connection with the accompanying drawing wherein:

The sole figure in the case is a schematic flow diagram of an integrated process for the thermal demethylation of methylcyclohexane to cyclohexane and toluene and the hydrogenation of the toluene to methylcyclohexane.

Briefly, we propose a process for making cyclohexane comprising the steps of combining fresh toluene feed with recycled toluene and cyclohexane; passing said combination of toluene and cyclohexane to a thermal hydrogenation zone; hydrogenating said toluene to methylcyclohexane in the presence of a suitable hydrogenation catalyst and hydrogen; withdrawing from said hydrogenation zone efiluent comprising methylcyclohexane and cyclohexane; recovering cyclohexane from said efiluent; passing said methylcyclohexane to a dealkylation zone; dealkylating said methylcyclohexane to cyclohexane in the 6 Claims 3,420,908 Patented Jan. 7, 1969 presence of hydrogen and a suitable dealkylation catalyst; recycling said toluene and cyclohexane to the hydrogenation zone. The overall yield of cyclohexane is greatly improved by following this sequence of steps.

Referring now to the drawing, toluene is introduced via line 1 and combined with toluene present in a recycle line 5. Hydrogen is supplied from a source not shown via line 3 and is introduced via line 7 along with the toluene into a catalytic hydrogenation reactor 9. The hydrogen to toluene mol ratio in reactor 9 is maintained preferably between the range of 0.3 to 1 to 10 to 1. Reactor 9 contains a fixed bed of catalytic material, such as platinum, palladium, and nickel, or combinations thereof supported in any suitable manner in the form of pellets or granules on alumina, silica, zirconia, diatomaceous earth, kieselguhr, or the like. The reactor 9 can operate at about 300- 700 p.s.i.a., typically about 475 p.s.i.a. and 300600 F., preferably around 385 F. The reactor efiluent is withdrawn from reactor 9 via line 11 and passed to a separa tion column 13 wherein gaseous hydrogen is removed as overhead in line 15, passed through compressor 14 and combined with the recycle line '5. Some or all of this hydrogen can also be sent through line 17 into a demethylation zone 19 which will be described in greater detail hereinafter.

In separator 13 bottoms comprising mainly methylcyclohexane and cyclohexane is withdrawn via line 18 and passed to a fractionating zone 21 wherein the light vaporous factions are removed from the overhead via line 23 to a suitable cyclohexane recovery unit (not shown). The light factions in line 23 consists primarily of cyclohexane product and small amounts of C to C paraffins.

A liquid methylcyclohexane phase is withdrawn from the bottom of the fractionator via conduit 25 and combined with the hydrogen in conduit 17 and passed into a demethylation zone 19. The demethylation zone is operated at a temperature range of from 500 to 600 F. and a pressure range of from 50 to 200 p.s.i.a. and the methylcyclohexane to hydrogen mol ratio is maintained in a range of from 1: 1 to 1:5.

Any well-known dealkylation catalyst can be employed in the demethylation zone. For example a catalyst comprising a metal selected from the group consisting of platinum, palladium and nickel having a particle size ranging from to +225 mesh supported on a base selected from the group consisting of alumina, silica, zirconia, diatomaceous earth and kieselguhr can be employed. It is preferred to operate in a fluidized bed within the demethylation zone.

The efiluent from zone 19 is removed via line 27 to a separator 29. Separator 29 serves as a liquid surge tank and a means to separate liquid and vapor phases. The vapor phase contains the bulk of the normal gaseous materials, hydrogen and methane, and is passed out the top of separator 29 and recycled to the demethylation zone 19 via conduit 31. A slipstream 35 is used to periodically remove methane from the system. The condensed material comprising toluene, methylcyclohexane, cyclohexane and some C to C parafiins is withdrawn from separator 29 via recycle line 5 and recycled to the hydrogenation zone 9.

The various aspects of our invention will now be illustrated by the following example which should be read in connection with the figure and the materialbalance set forth in Table I.

Example Toluene feed is introduced via conduit 1, mixed with hydrogen supplied via conduit 3 and with toluene recycled via conduit 5, the mixture is passed via conduit 7 to hydrogenation reactor 11. In reactor 9 the toluene is catalytically hydrogenated in the presence of a fixed bed of Harshaw catalyst type R-1124 (nickel supported on kieselguhr and aluminum). Elfluent is withdrawn from reactor 9 at 445 F. and 465 p.s.i.a. and it is passed via conduit 11 to separator 13, from which a gaseous mixture comprising hydrogen and methane is Withdrawn via line 15 a portion of which is combined with recycle line and a portion of which is sent via line 17 to the demethylization zone 19. A liquid stream comprising methylcyclohexane is withdrawn from separator 13 via line 18 and it is passed to fractionator 21. Cyclohexane, methane and other products are withdrawn from the top of fractionator 21 via conduit 23 and passed to suitable cyclohexane recovery system (not shown). Bottoms is withdrawn comprising methylcyclohexane and passed via conduit 25 combined with hydrogen in conduit 17 and passed to a demethylation zone 19. The methylcyclohexane is demethylated in a fluidized bed catalyst system using a range of -180 to +325 mesh catalyst. The catalyst corn prises nickel deposited on kieselguhr which is similar to that used in the hydrogenation of the toluene. The reaction is carried out at a temperature of 530 F. Considerable toluene is also formed in this reaction. The pressure is 200 p.s.i.a. and the mol ratio of methylcyclohexane to hydrogen is maintained about 1-3. The efliuent is withdrawn from the demethylation reaction zone 19, passed via conduit 27 to a flashing zone 29 wherein hydrogen and methane is flashed from the liquid mixture and recycled via conduit 31 to the demethylation zone 19. The liquid efliuent from flash zone 29 is passed via recycle conduit 5 and combined with fresh toluene and hydrogen in the hydrogenation zone 9.

By an observation of the material balance set forth hereinbelow it is readily apparent that 70 percent of the toluene fed to the system is eventually recovered as cyclohexane and that the demethylation reaction can be carried out at conditions favorable to the maximum formation of cyclohexane without lowering the overall efliciency of the operation.

What is claimed is:

1. A process for making cyclohexane comprising the steps of combining fresh toluene feed with recycled toluene and cyclohexane; passing said combination of toluene and cyclohexane to a thermal hydrogenation zone; hydrogenating said toluene to methylcyclohexane in the presence of a suitable hydrogenation catalyst and hydrogen; withdrawing from said hydrogenation zone efl'luent comprising methylcyclohexane and cyclohexane; recovering cyclohexane from said effluent; passing said methylcyclohexane to a dealkylation zone; dealkylating said methylcyclohexane to cyclohexane in the presence of hydrogen and a suitable dealkylation catalyst; withdrawing from said hydrodealkylation zone eflluent comprising toluene and cyclohexane; recycling said toluene and cyclohexane to the hydrogenation zone.

2. A process according to claim 1 further including the step of purging methane from said dealkylation efiiuent.

3. A process according to claim 1 wherein the hydrogenation catalyst comprises a metal selected from the group consisting of platinum, palladium, and nickel or combinations thereof, said metal being supported on a base selected from the group consisting of alumina, silica, zironia, diatomaceous earth and kieselguhr, said process being further characterized in that the hydrogenation is conducted at a pressure ranging from 300 to 700 p.s.i.a. and a temperature ranging from 300600 F.

4. A process according to claim 1 further characterized in that the hydrogen to toluene mol ratio is maintained in a range of from 0.3:1 to 10:1 in the hydrogenation zone.

5. A process according to claim 1 further characterized in that the catalyst in the demethylation zone comprises a metal, having a particle size ranging from l to +225 mesh, is selected fromthe group consisting of platinum, palladium and nickel supported on a base selected from the group consisting of alumina, silica, zirconia, dia- TABLE I Stream Toluene Hydrogen Feed to Hydrogen Flash Flash Hydrogen Frac- Frac- Component Feed Feed Recycle Hydro- Effluent Separator Separator Recycle tionator tionator genator Bottoms Overhead Overhead Bottoms Stream Number Hydrogen 2, 473 Trace 2, 473 1, 193 Trace Methane Trace Trace Trace Trace 0 Parafiins 151 151 151 151 C Paraffin 352 352 352 352 C Parafiins 1, 820 1, 820 1, 820 1,820 Methyleyclopentane 510 510 510 cyclohexane 6, 450 6, 450 6, 450 6, 450 Methylcyelohexane 50, 200 50, 200 69, 800 69, 800 Toluene 9, 200 120 18, 320

Totals, lbsJhr 9, 200 2, 473 68, 603 80, 276 80, 276 79, 083

Stream Demethylation Recycle of Demeth late Overhead from Methane P Component Feed Overhead Efliue r rt Separator 29 urge Stream Number 17+25+31 31 27 3l+35 35 Hydrogen 6, 93 5, 000 5, 400 5, 400 400 Methane 39, 39, 100 2, 900 C Paraffins. 151 Trace Trace 0 Paraflins- 352 C Parafiins 1 820 Methylcyclopentane 510 cyclohexane 6 450 Methylcyclohexane. 50: 200 Toluene Totals, lbs/hr 113, 103 113, 103 44, 500 3, 300

Obviously, many modifications and variations of the present invention are possible in the light of the above teachings. It is therefore to be understood that within the scope of the appended claims the invention may be practiced otherwise than as specifical y 19 ibcl herein.

tomaceous earth, kieselguhr, and the like, and the temperature is maintained in a range of from 500 to 60'0" F. and the pressure in the range of from 50 to 200 p.s.i.a. and a methylcyclohexane to hydrogen mol ratio in the range of from 1:1 to 1:5.

6. A process according to claim 5 further characterized in that the catalyst in the demethylation zone is a fluidized bed system.

References Cited 2,422,674 6/1947 Haensel et a1. 260666 2,441,663 5/1948 Haensel et a]. 260666 6 2,898,387 8/1959 Teter 260--667 3,213,150 10/1965 Cabbage 260667 3,253,048 5/ 1966 Cabbage 260-667 DELBERT E. GANTZ, Primary Examiner.

VERONICA OKEEFE, Assistant Examiner.

US. Cl. X.R. 260--666, 672 

1. A PROCESS FOR MAKING CYCLOHEXANE COMPRISING THE STEPS OF COMBINING FRESH TOLUENE FEED WITH RECYCLED TOLUENE AND CYCLOHEXANE; PASSING SAID COMBINATION OF TOLUENE AND CYCLOHEXANE TO A THERMAL HYDROGENATION ZONE; HYDROGENATING SAID TOLUENE TO METHYLCYCLOHEXANE IN THE PRESENCE OF A SUITABLE HYDROGENATION CATALYST AND HYDROGEN; WITHDRAWING FROM SAID HYDROGENATION ZONE EFFLUENT COMPRISING METHYLCYCLOHEXANE AND CYCLOHEXANE; RECOVERING CYCLOHEXANE FROM SAID EFFLUENT; PASSING SAID METHYLCYCLOHEXANE TO A DEALKYLATION ZONE; DEALKYLATING SAID METHYLCYCLOHEXANE TO CYCLOHEXANE IN THE PRESENCE OF HYDROGEN AND A SUITABLE DEALKYLATION CATALYST; WITHDRAWING FROM SAID HYDRODEALKYLATION ZONE EFFLUENT COMPRISING TOLUENE AND CYCLOHEXANE; RECYCLING SAID TOLUENE AND CYCLOHEXANE TO THE HYDROGENATION ZONE. 